The present invention relates generally to reactive force control apparatus for controlling a reactive force responsive to operation of a pedal of an electronic keyboard instrument, and more particularly to an improved reactive force control apparatus for a pedal of an electronic keyboard instrument which can achieve an operational feeling of the pedal approximate to that of a natural keyboard instrument, such as an acoustic piano.
The acoustic pianos have a mechanism for generating a tone by causing a hammer to strike a string in response to depression of a key, and the thus-generated tone differs in its sounding manner and volume depending on an intensity and speed of the key depression. Further, the acoustic pianos have pedals for controlling resonance of a tone; the grand pianos, for example, have a damper pedal, sostenute pedal and soft pedal.
The damper pedal is a pedal that controls dampers for stopping vibrations of strings. The dampers are provided in one-to-one corresponding relation to the strings. Each of the dampers is connected to the damper pedal (hereinafter sometimes referred to as “pedal”) via some connecting portions. Once the pedal (damper pedal) is pushed or pressed down, all of the dampers corresponding to the strings are released, so that, even if a human player releases its finger from an operated key, tone deadening by the corresponding damper does not take place and thus the tone of the depressed key remains sounding for a given time. In this case, all of the strings, including those corresponding to non-depressed keys, resonate so that harmonics sound clearly. Thus, the human player can impart various expression to tones generated by the piano.
Further, so-called “play” is provided in the connecting portions between each of the dampers and the pedal. With such play, the human player can not only have his or her foot always placed on the pedal but also perform so-called half pedal operation of lightly pushing or pressing down the pedal to a partway position such that the damper slightly retrains the string. With the pedal pressed down lightly, the damper does not operate and is pushed up only when the pedal is pressed down to a predetermined position. Thus, a reactive force (i.e., load on the human player's foot) due to the pressing-down of the pedal suddenly starts varying stepwise at the time point when the pushing-up of the damper is started.
Among electronic keyboard instruments emulating tone colors, operability and outer appearances of the aforementioned acoustic pianos are electronic pianos. Among such electronic pianos are ones equipped with three pedals functioning similarly to the damper pedal, sostenute pedal and soft pedal of the grand piano. The electronic pianos, however, do not have to perform an operation for releasing a damper from a string because they do not generate a tone by actually striking the string. Instead, the electronic pianos are constructed to electronically perform a process corresponding to pedal operation so as to generate a tone equivalent to that generated by the pedal operation. Thus, in the electronic pianos, a pedal device itself is simple in mechanism; for example, a springs etc. are provided between the pedal pivotably mounted to a frame and a bottom plate so that upward reactive force is normally imparted to the pedal by the biasing force of the spring.
In one known example of the pedal devices of the electronic pianos, the pedal is normally urged by a single spring, as disclosed in Japanese Patent Application Laid-open Publication No. 2001-22355. With the biasing force of the single spring, however, it is not possible to produce stepwise variation of a reactive force like that produced at the time of the damper push-up in the grand piano. Consequently, if a human player experienced in playing an acoustic piano plays the electronic piano, the human player may feel uncomfortable due to a difference in playing feeling and can not grasp a half pedal position sensuously.
Thus, Japanese Patent Application Laid-open Publication No. 2004-334008 discloses an improved pedal device, which includes first and second springs so that a biasing force of the first spring alone and a combined biasing force of the first and second springs are sequentially imparted to the pedal in response to a changing displaced amount of the pedal in such a manner that the reactive force of the pedal can change or vary in a stepwise manner. Although the combination of the biasing forces of the plurality of springs permits stepwise variation of the reactive force, the biasing forces of the springs can provide only one distribution pattern of reactive force intensities, and thus, the reactive force can not be varied or changed as desired in response to an input setting and/or actual operation by a human player.
Further, a reactive force control apparatus disclosed in Japanese Patent Application Laid-open Publication No. 2006-146259 includes a solenoid for driving an operating member in the form of a key, and a reactive force control section for controlling the solenoid. With such an arrangement, it is possible to adjust an operating feeling of the operating member through an electric driving force and vary a reactive force to the operating member in response to actual operation of the operating member. However, because the reactive force control apparatus disclosed in the No. 2006-146259 publication generates solenoid driving instructing values on the basis of a table selected from among a plurality of tables, a human player can not set the reactive force of the operating member at a position and intensity desired by the human player itself. Thus, the operational feeling of the operating member can not be varied freely by the human player.